Exemplary embodiments of the present invention relate to a stacked microstrip antenna.
The technical literature (e.g. R. B. Waterhouse, Ed., “Microstrip Patch Antennas—A Designers Guide”, Kluwer Acad. Publishers, 2003, p. 90), discloses that in order to obtain a wide impedance bandwidth the electromagnetic coupling of the two microstrip antenna elements (also designated hereinafter as patch elements for short) of the antenna that lie one above the other should only be permitted to be weak. The technical consequence is that RF foam materials are used as separator and carrier between the two patch elements, since foams of this type have a low relative permittivity ∈r. Such a solution with RF foam materials is known from U.S. Pat. No. 7,636,063 B2. However, these foams are too temperature- and pressure-sensitive for standard PCB processes, which results in complicated and costly production methods.
U.S. Pat. No. 7,636,063 B2 also describes a further approach, in which the interspace between the two patch elements is completely formed by a cavity. The resulting necessary outer carrier for one of the two patch elements is embodied as a housing or radome. This likewise leads to complex and costly production methods.
ZIVANOVIC, B.; WELLER, T. M.; MELAIS, S.; MEYER, T.; “The Effect of Alignment Tolerance on Multilayer Air Cavity Microstrip Patches”, IEEE Antennas and Propagation Society International Symposium, 381-384, Jun. 9-15, 2007, doi: 10.1109/APS.2007.4395510; describes a microstrip antenna composed of an individual microstrip antenna element above a ground surface, wherein the intervening dielectric separator has a cavity.
LAGER, I. E.; SIMEONI, M.: “Experimental Investigation of the Mutual Coupling Reduction by Means of Cavity Enclosure of Patch Antennas”, First European Conference on Antennas and Propagation, Nov. 1-5, 6-10 2006, doi: 10.1109/EUCAP.2006.4584577; describes a technique for decoupling individual microstrip antennas of an RF group antenna that are arranged alongside one another on an RF printed circuit board. In this case, the individual microstrip antennas are each surrounded by plated-through holes.
U.S. Pat. No. 7,050,004 B2 describes a microstrip antenna whose ground surface is formed by a movable membrane, the position of which relative to the microstrip antenna element can be altered by applying a voltage.
U.S. Pat. No. 5,363,067 A describes a microstrip line comprising two conductors lying alongside each other above a ground surface. The space above the two conductors is formed by a respective cavity within a dielectric substrate.
Exemplary embodiments of the present invention provide a stacked microstrip antenna that is advantageous in terms of production engineering, without the necessary weak electromagnetic coupling of the patch elements being lost.
According to the invention, a separator is arranged between the two patch elements lying one above the other and air cavities are introduced into the separator, e.g., by drilling or milling.
As a result, it is possible to use a separator material that is advantageous in terms of production engineering, even if its relative permittivity ∈r is not optimum (i.e., relatively high) with regard to the desired weak coupling between the patch elements. The necessary matching is effected by the cavities introduced into the separator, which significantly reduces the effective relative permittivity between the patch elements. This results in a significant reduction of the electromagnetic coupling of the patch elements.
The separator according to the invention thus reduces to a type of holding frame for the structure of the antenna, while the air cavities significantly decrease the effective relative permittivity between the patch elements.
Particularly advantageously, a conventional RF printed circuit board base material (e.g., RO 4003® C from the Rogers Corporation, Microwave Materials Division, 100 S. Roosevelt Avenue, Chandler Ariz. 85226-3415, USA) can be used as separator. Such materials usually consist of a resin with glass fiber inserts introduced therein. They have a good stability and are unproblematic in terms of production engineering. The comparatively high relative permittivity of these materials in relation to an RF foam material is compensated for by the introduced cavity or plurality of cavities.
The following advantages, in particular, are achieved by means of the invention:                an increase in the bandwidth of the antenna is made possible by the low effective relative permittivity.        it is possible to use standard RF materials and standard PCB processes for antenna production, such that cost-effective production methods are made possible.        the availability of robust and broadband antennas is made possible.        independence from complex antenna solutions, based on RF foams, that are technically difficult to produce.        diverse application of this technology e.g., as emitter elements for 3D-T/R modules or as circularly polarized, structure-integrated antennas.        useable in principle for a wide frequency range.        